The present day tennis shoe is typically constructed with a thick outsole/midsole unit of molded rubber and/or foamed polymeric material, which extends throughout the full length of the shoe for cushioning the foot and protecting it against impacts. In addition, the midsole unit usually embodies a cushioning heel wedge extending along the midfoot and rearfoot regions. The heel wedge provides the heel lift which is desired for running.
Because of its thick cushioning, the foregoing sole construction amply meets the wearer's comfort requirements. However, this construction has now been found to have certain significant drawbacks for playing tennis and other court games involving similar footwork.
First of all, the foregoing sole construction abnormally restricts the natural foot motions required to perform various tennis maneuvers which involve more than just straight ahead running. For example, the tennis player frequently springs or crouches on the balls or toes of his feet, makes abrupt stops after pushing off and sprinting short distances, pivots or turns sharply on the ball of one foot or the other, skips or runs sideways, and makes abrupt changes in direction of movement. The wide variety of foot motions required to execute these maneuvers is hampered by the foregoing sole construction mainly because it stiffens the shoe significantly in the midfoot region to inhibit the extent to which the forefoot and rearfoot can act independently of each other.
Additional problems arise from the fact that the foregoing sole construction places the foot at a significant height (Usually one inch or more at the heel) above the ground surface. For example, the higher the foot is above the ground the more difficult it is for the player to balance himself and to maintain his stability in executing the tennis maneuvers mentioned above. Furthermore, the forces acting on the foot and also the force moments about the foot joints are increased as the height of the foot above the ground is increased.
In addition, the likelihood of jamming or twisting the foot during a stopping maneuver is increased as the height of the foot above the ground is increased, especially with shoe constructions having sharp outsole edges. If the forces are applied to the foot joint before full foot support is attained in a stopping maneuver, unnatural conditions tend to arise and may lead to injuries. For example, upon stopping a lateral motion, the outer edge of the shoe may catch on the court, causing the shoe to roll over, thereby increasing the likelihood of ankle sprains. In stopping a forward motion, a high heel, especially one having relatively sharp edges, tends to catch on the court surface to increase the impact of the forefoot on the court surface. Finally, increasing the height of the heel above the ground increases the angle through which the wearer must lean in a forward direction to lift the heel and to lock the midfoot for propelling himself. If the player attempts to pivot while his heel is down on the ground, the resulting heel traction causes the foot to lock up to apply an objectionable torque to the knee.
Aside from the thickly cushioned sole construction described above, other shoe parts contribute to the restriction of natural foot movements. For example, medical longitudinal arch supports and lateral edges tend to increase the stiffness of the shoe in the midfoot region.
In addressing the foregoing problems, it was recognized that the natural foot motion required for tennis and other court games are best achieved with bare feet without introducing any artificial constraints on the foot motions and without elevating the foot above ground level. Therefore, the optimum solution to the foregoing problems is to eliminate the shoe altogether and to play barefooted. However, the obvious drawback to such a solution is that playing barefooted on hard court surfaces for any prolonged period of time is uncomfortable and hard on the feet.